S-Adenosylhomocysteinase. The mechanism of inactivation of SAHase by 2'dAd will be investigated. 2'3H dAd will be synthesized in order to determine whether 3H is released during inactivation. Uniformly labeled C14 2-d'Ad will also be synthesized to determine the fate of the sugar moiety of 2'dAd subsequent to inactivation. B12-Coenzyme. C-5' chirally labeled B12-coenzyme has been synthesized. Experiments will be carried out to determine whether racemization occurs when the coenzyme is bound to the enzyme under anaerobic conditions. This will be done by NMR spectroscopy. 1-P, 5-S-Me-ribose hydrolase. This enzyme will be isolated and its mechanism of action examined. 1-P, 5-S-Me-ribose is derived from S-Me-adenosine. The enzyme will be isolated and purified and its reaction mechanism will be examined. Initial questions to be answered are: Is O2 required? Does the enzyme contain NAD?